In recent years, engine blocks for use in motor vehicles, ships, air crafts and the like are often manufactured using lightweight aluminum instead of cast iron. As compared with a cast-iron engine block, an aluminum engine block is high-priced but is advantageous in that it is possible to significantly reduce the weight of the engine block.
However, due to the intrinsic properties thereof, aluminum is hardly used as a cylinder liner on which a high temperature and a high pressure act. Accordingly, even if an engine block is made of aluminum, a cast iron liner exhibiting a superior wear resistance is used as a cylinder liner. Thus, a cylindrical cast iron liner is fixed to an engine block mold and, then, molten aluminum is poured into the engine block mold, thereby integrating an aluminum engine block and a cast iron liner.
An aluminum engine block is usually manufactured by a die casting method. The die casting method is a casting method used in casting nonferrous metal. In the die casting method, molten metal is injected into a die at a pressure equal to or higher than the atmosphere pressure and is continuously pressed by a plunger until the molten metal is completely solidified.
The die casting method has been used in casting metal types. Along with the development of nonferrous metal having high, strength, the range of application of the die casting method is gradually widened.
A mold employed in the die casting method suddenly makes contact with a high-temperature molten metal. Thus, corrosions or cracks are easily generated on the surface of the mold. For that reason, special steel having a high heat resistance is primarily used in making a die-casting-purpose mold.
In order to perform a die casting process, it is necessary to use a die casting machine for pressurizing and injecting molten metal. The die casting machine is designed to inject molten metal into a mold at a high pressure and a high speed using a compressed air or a hydraulic plunger.
For the reasons stated above, the die casting method is more costly than an ordinary casting method and is not suitable for production of a small number of articles. The die casting method is economical only when mass-producing the same kind of products.
Depending on the method of injecting molten metal, die casting machines may be classified into a hot-chamber-type die casting machine and a cold-chamber-type die casting machine.
In the hot-chamber-type die casting machine, a pressurizing cylinder is disposed within a melting pot. A plunger is moved into the pressurizing cylinder by a pneumatic pressure, a hydraulic pressure or an oil pressure, thereby pushing molten metal into a mold. Aluminum engine blocks are primarily manufactured by the hot-chamber-type die casting machine. In the hot-chamber-type die casting machine, there is a need to preheat an engine block mold prior to casting. During a casting process, a constant temperature (e.g., 250 to 300 degrees C.) should be maintained in order to minimize generation of detective products.
On the other hand, a melting furnace is independently provided in the cold-chamber-type die casting machine. Molten metal is taken out of the melting furnace and is put into a pressurizing chamber. The molten metal is pushed into a die by a plunger. That is to say, in the cold-chamber-type die casting machine, molten metal is put into a sleeve made of special steel. By moving a piston rod, molten metal is injected into a die with a plunger mounted to the front end of the piston rod.
As compared with the hot-chamber-type die casting machine, the cold-chamber-type die casting machine has an advantage in that impurities are less likely to infiltrate into the molten metal and a dense structure can be obtained by applying a high pressure at an initial cooling stage and during a solidifying period.
Depending on the method of moving a die, die casting machines may be divided into a vertical die casting machine and a horizontal die casting machine.
In the vertical die casting machine, a movable die is vertically disposed on a fixed die. In the horizontal die casting machine, a fixed die and a movable die are horizontally disposed. While the vertical die casting machine has been extensively used in the past, the horizontal die casting machine is predominantly used in recent years.
FIGS. 1 and 2 illustrate one example of an aluminum engine block 10 manufactured by the aforementioned die casting method. As illustrated in FIGS. 1 and 2, the aluminum engine block 10 includes a body made of aluminum and a cast iron liner 20 having a superior wear resistance. In FIG. 2, reference numeral 30 designates a water jacket for cooling an engine.
A process of manufacturing a conventional aluminum engine block will now be described with reference to FIGS. 3 and 4.
An aluminum engine block 10 is automatically manufactured by a die casting machine in an ordinary continuous casting line. As illustrated in FIG. 3A, an engine block mold M is mounted to a die. Thereafter, as illustrated in FIG. 3B, a bore pin 40 is fitted to the engine block mold M. The bore pin 40, which serves as a core during a casting process, is configured to support a cast iron liner 20 when pressurizing molten aluminum.
Then, as illustrated in FIG. 30, the cast iron liner 20 is fitted to the outer circumferential surface of the bore pin 40 using a robot arm 50. The cast iron liner 20 is formed in a cylindrical shape so as to have a predetermined thickness. After the casting process, the inner circumferential surface of the cast iron liner 20 is machined. A plurality of cast iron liners 20 is disposed side by side along a casting line. In the case where an engine block is of a four-cylinder type, the robot arm 50 picks up four cast iron liners 20 and fits the cast iron liners 20 to the outer circumferential surfaces of bore pins 40.
Then, if molten aluminum is pressurized in the state illustrated in FIG. 3D, the molten aluminum is brought into contact with the outer circumferential surface of the cast iron liner 20 and is solidified.
If an engine block product is taken out by moving the mold M after the molten aluminum is solidified, it is possible to obtain an engine block in which a cylindrical cast iron liner is integrally formed with an aluminum body.
However, in the conventional aluminum engine block manufacturing method described above, defects are often generated in a boundary region between the cast iron liner 20 and the aluminum engine block 10. Since cast iron and aluminum differ in physical and chemical properties such as a melting point or the like from each other, it is difficult for cast iron and aluminum to be completely fused in a boundary region thereof. Thus, casting defects are frequently generated in the boundary region.
The defective engine block is discarded or recycled. In the case of discarding the defective engine block, a loss of material cost grows larger. In the case of recycling the defective engine block, a large amount of cost is incurred in the recycling process.
If it is possible to easily remove the cast iron liner 20 from the defective engine block 10, no problem will be posed in recycling the defective engine block 10 into an aluminum ingot. However, it is not easy to remove the cast iron liner 20 integrally formed with the engine block 10.
If the defective engine block is melted and recycled into an aluminum ingot without completely removing a cast iron component, the quality of the aluminum ingot is reduced due to the cast iron component remaining in the aluminum ingot. In order to solve this problem, it is thinkable to remove a cast iron component from molten aluminum. In this case, however, a large amount of cost is incurred.
As a solution to the aforementioned, problem, Korean Patent Application Publication No. 10-2006-0131064 discloses a method of detaching and recovering a cylinder liner from a cylinder block. In this method, a cylinder block for an automotive engine to be recycled is loaded onto a conveyer. Then, the inner surface of a cylinder liner is heated by flames or induction heating. Particularly, a boundary region between an aluminum body and a cylinder liner of the cylinder block is heated to a temperature equal to or higher than a melting point of the aluminum body, thereby removing the cylinder liner.
In the conventional method mentioned above, however, an additional heat source is needed, in order to heat the inner surface of the cylinder liner by flames or induction heating. This poses a drawback in that a recycling apparatus becomes complex. Furthermore, it is difficult to completely remove a cast iron component even if the cylinder liner is heated and melted.
Korean Patent No. 10-0625109 discloses an apparatus and method of removing a liner from an aluminum cylinder block. In this prior art, a defective product generated in a cylinder block manufacturing process is recycled into a raw material for the production of a cylinder block without going through an additional smelting process.
To this end, the apparatus for manufacturing a cylinder block including a cylinder body made of aluminum and a liner made of another metallic material and fixed to the inner surface of the cylinder body includes a bed, a movable base installed so as to reciprocate toward and away the bed, a fixing means for fixing a detective cylinder block to one of the bed and the movable base, a cutting tool mounted to the other of the bed and the movable base at the opposite side of the cylinder block in a position corresponding to the cylinder of the cylinder block, the cutting tool having a cutting diameter larger than the outer diameter of the liner, a rotating means for rotating the cutting tool, and a moving means for moving the movable bas toward the bed so that the liner of the cylinder block and the peripheral portion thereof are cut by the cutting tool.
The apparatus of the prior art cited above is designed to remove the cylinder liner through a cutting work in the case where defects are generated in the cylinder block. However, the apparatus of the prior art is extremely complex due to the provision of the additional cutting tool. In addition, there is a limit in removing the cylinder liner through the cutting work.